Thermography is an image-forming process including a heating step and hence includes photothermography in which the image-forming process includes image-wise exposure and direct thermal processes in which the image-forming process includes an image-wise heating step. In direct thermal printing a visible image pattern is produced by image-wise heating of a recording material.
Thiazoline-2-thione and benzothiazoline-2-thione compounds are well-known as toning agents in silver halide DTR photographic materials in which they are used in a liquid developer, see for example GB 1,101,927, U.S. Pat. No. 3,433,640 and U.S. Pat. No. 3,702,246, and in silver halide photographic materials as toning agents in combination with different stabilizers, see for example U.S. Pat. Nos. 3,418,131, 3,666,471, JP 07-306492 and JP 11-202444. Furthermore, U.S. Pat. No. 3,620,749 discloses photosensitive compositions comprising silver complexes of 3-alkyl-benzothiazoline-2-thiones in association with 2-mercapto-1,3,4-oxadiazole derivatives and photosensitive elements comprising such compositions.
JP 11-202444 discloses a heat-developing sensitive material characterized by containing at least one sort of compound represented by the following general formulae (1), (2) or (3):
X is an atomic group necessary to form a hetero ring substituted by at least one of —SO3M, —COOM, and —OM groups; X is an atomic group substituted by at least one of —SO3M, —COOM, or —OM and in which heterocycle formation is possible; M represents a hydrogen atom, a metal atom, a quaternary ammonium or phosphonium group; but does not have the substructure —NH—C(═S)— in the heterocyclic structure;
A1 and A1′ represent a —SO3M, —COOM, or —OM group and M represents a hydrogen atom, a metal atom, a quaternary ammonium or phosphonium group. Even if A1 and A1′ are the same, they may differ; m represents an integer of 1–10; A2 and A2′ represent an electron withdrawing groups, and even if A2 and A2′ are the same, they may differ; n represents an integer of 1–10; each of A3 and A3′ represents a functional group containing a S, Se or Te atom which may be combined with a complex ion, and even if A3 and A3′ are the same, they may differ; r is 0 or 1; Y, Y1, and Y2 represent an aliphatic, aromatic or heterocyclic group; Z is an S, Se or Te atom; and p is 1 or 2.
JP 11-202444 further discloses:
I-6 I-7 I-8I-9 I-10 I-11 I-12 I-13 I-14
U.S. Pat. No. 4,451,561 discloses a heat-development-type recording material comprising on a support a heat-development-type image recording layer containing: (a) an organic silver salt, (b) a reducing agent, (c) a binder, and (d) at least one amido derivative of a 5-mercapto-1,3,4-triazole or a 5-mercapto-thiadiazole.
U.S. Pat. No. 3,080,254 discloses a typical heat-sensitive copy paper including in the heat-sensitive layer a thermoplastic binder, e.g ethyl cellulose, a water-insoluble silver salt, e.g. silver stearate and an appropriate organic reductor, of which 4-methoxy-1-hydroxy-dihydronaphthalene is a representative. Localized heating of the sheet in the thermographic reproduction process, or for test purposes by momentary contact with a metal test bar heated to a suitable conversion temperature in the range of about 90–150° C., causes a visible change to occur in the heat-sensitive layer. The initially white or lightly coloured layer is darkened to a brownish appearance at the heated area. In order to obtain a more neutral colour tone a heterocyclic organic toning agent such as phthalazinone is added to the composition of the heat-sensitive layer.
U.S. Pat. No. 3,885,967 discloses a photosensitive material for a thermally developable lightsensitive element, which comprises: a) a silver salt component comprising silver laurate or silver caprate, b) a catalytic amount of a photosensitive silver halide component comprising a photosensitive silver halide, or a compound which reacts with silver laurate or silver caprate to form a photosensitive silver halide, c) a reducing agent, d) a binder, and e) a toning agent comprising a compound represented by the formula:
wherein R1, R2, R3 and R4 each represents a hydrogen atom, an alkyl group, an aryl group, an acylamido group, a halogen atom, a hydroxyl group or a nitro group.
EP-A 0 752 616 discloses a thermographic material comprising at least one element and wherein said element(s) contain(s) therein a substantially light-insensitive organic heavy metal salt and an organic reductor therefor, the said material being capable of thermally producing an image from said organic heavy metal salt and reductor, wherein said material contains a 1,3-benzoxazine-2,4-dione toning agent having general formula (I):
wherein R1 represents hydrogen, —CH2OH, —(C═O) —R, —CONHR, or M; R2, R3, R4 and R5 each independently represents hydrogen, —O— (C═O) —OR or —NH— (C═O) —OR and at least one of which is not hydrogen if R1 is also hydrogen; R represents an alkyl or aryl group either of which may be substituted; and M represents a monovalent heavy metal ion.